In recent years, in the medical field, a capsule endoscope (see, for example, Non-Patent Document 1) has begun to be used to carry out an image examination of the digestive organs. It is considered at present that a capsule endoscope is effective for an examination of the small intestine which has been difficult to capture in video using a conventional probe-type endoscope.
However, it takes about eight hours for a capsule endoscope to be passed through the small intestine which is approximately five to six meters long when extended. Accordingly, the entire eight-hour video obtained by the capsule endoscope becomes a target of examination, placing the burden on a doctor who carries out the examination. Hence, at present, the examining doctor performs manual operations for high- and low-speed playback while observing a video and staring at the video so as not to overlook a sudden, unpredictable change, that is, the appearance of the lesion. In view of this, there is a demand for short-time video display that reduces a burden on the examining doctor and enables him/her to maintain concentration to avoid oversight.
While in the current probe-type endoscope, the digestive organs are observed by inserting a probe, the capsule endoscope allows a capsule that is swallowed by a test subject to be propelled by peristaltic movement of the digestive organs, as with the passing of food, and a video is continuously shot as long as a battery lasts. The movement of the capsule is advanced according to the physical condition of the test subject, as with the movement of food, and thus such examination is not burdensome for the test subject. However, since image capturing takes a long time, the examining doctor needs to examine such video for a long time. However, in practice, since the movement of a capsule is slow, it is often the case that very similar images continue for a long time.
In display of such an image sequence, even if frames are advanced at a speed higher than a normal speed, it does not cause any problem in examination, and thus at present, the examining doctor performs fast-forwarding by an interactive operation. In the current operation, the doctor performs, by his/her decision, fast-forwarding with respect to a frame rate which is a constant speed, and thus, fast-forwarding is limited so as to prevent the doctor from overlooking the legion when a sudden movement of a capsule or a sudden movement of the small intestine occurs. In addition, when fast-forwarding speed exceeds the limitations, there is the complexity of having to rewind the video, reduce the speed, and restart the examination. In addition, in order not to overlook a big change in a partial area at the time of fast-forwarding, the doctor is required to concentrate heavily, which is a significant burden on him/her. Thus, it takes about three hours for a beginner of an examination to carry out an examination of an eight-hour video and it takes about one hour even for a skilled person to carry out such an examination. Accordingly, there is a demand for a support technique for realizing an examination that takes only a short time.
Meanwhile, in video processing, it is possible to automatically detect its state. Such a technique is used as a technique for detecting a cut point in a video. In conventional cut point detection, a shot cut is detected by determining how many blocks have similarity in the whole image, based on a square sum of differences between luminance values of small blocks in adjacent images (see, for example, Non-Patent Document 2) and a similarity between histograms of blocks (see, for example, Non-Patent Document 3), or the like. However, this technique is intended to determine whether there is a cut and is not intended to convert a similarity between consecutive adjacent images into numbers and change the display speed. A method has also been proposed for changing the frame-to-frame rate based on MPEG (Moving Picture Experts Group) motion compensation information (see, for example, Patent Document 1). However, this method is intended to reproduce video and sound contents while synchronizing sound and a video, so that a user can visually recognize the audio-visual contents. Hence, it is difficult to apply the method to short-time video display for preventing a doctor from overlooking the lesion. Non-Patent Document 1: “M2A(R) Capsule Endoscopy Given(R) Diagnostic System”, [online], Given Imaging Ltd., [searched on Mar. 9, 2005], the Internet URL is: http://www.givenimaging.com/NR/rdonlyres/76C20644-4B5B-496 4-811A-071E8133F83A/0/GI Marketing Brochure 2003.pdf. Non-Patent Document 2: B. Shahraray, “Scene change detection and content-based sampling of video sequences,” Proc. IS&T/SPIE 2419, pp. 2-13, 1995    Non-Patent Document 3: D. Swanberg, C.-F. Shu, R. Jain, “Knowledge guided parsing in video databases,” Proc. SPIE Conf. 1908, 1993, pp. 13-24.    Patent Document 1: Japanese Laid-Open Patent Application No. 10-243351